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Carbon nanotubes (CNTs) hold great promise in many fields because of their unique structures and properties. However, the preparation of CNTs generally involves cumbersome equipment and time-consuming processes. Here, we report an ultra-fast carbothermal shock (CTS) approach for synthesizing CNTs with a simple homemade setup by employing Joule heating of a carbon substrate. Carbonized silk fabric (CSF) loaded with transition metal salts in ethanol solution was used as the substrate, which was treated with a pulse voltage of 40 V for only 50 ms and then covered with uniform CNTs grown with bimetallic alloy catalyst nanoparticles (diameter: ∼ 9 nm). The temperature ramp rate is as high as 105 K/s. The as-obtained sample has a unique fluffy structure similar to the trichobothrium of spiders, endowing it versatile applications such as airflow sensors or air filters. The CTS technique presents an easy-accessible and highly efficient approach for synthesizing CNTs, which may be also applied in synthesizing other nanomaterials.

In order to prolong the service life of cement-based materials subjected to external chloride ion attacks, two kinds of methods, a surface treatment and chloride immobilization, were combined by fabricating a nanosilica-modified cement paste and coating it on mortar samples as a surface treatment material (HSM). The protective effect of the HSM was evaluated according to its surface hardness, and an RCM test was carried out, which indicated that the attached layer could both increase the surface hardness and decrease the chloride diffusion coefficient. Then, the chloride immobilization mechanisms were illustrated in terms of chloride blocking resistance, chemical binding and physical binding X-ray diffraction (XRD), and thermogravimetric/derivative thermogravimetric (TG/DTG) and thermodynamic modeling. The results showed that the hybrid nanomaterials that modified the cementitious surface treatment materials may effectively improve the chloride-resistant property of a matrix with content of no more than 1%. This research outcome could provide evidence that hybrid nanosilica can be applied in surface treatment technology.

Many natural materials possess built-in structural variation, endowing them with superior performance. However, it is challenging to realize programmable structural variation in self-assembled synthetic materials since self-assembly processes usually generate uniform and ordered structures. Here, we report the formation of asymmetric microribbons composed of directionally self-assembled two-dimensional nanoflakes in a polymeric matrix during three-dimensional direct-ink printing. The printed ribbons with embedded structural variations show site-specific variance in their mechanical properties. Remarkably, the ribbons can spontaneously transform into ultrastretchable springs with controllable helical architecture upon stimulation. Such springs also exhibit superior nanoscale transport behavior as nanofluidic ionic conductors under even ultralarge tensile strains (>1,000%). Furthermore, to show possible real-world uses of such materials, we demonstrate in vivo neural recording and stimulation using such springs in a bullfrog animal model. Thus, such springs can be used as neural electrodes compatible with soft and dynamic biological tissues.

Electrically conducting films are important for the development of modern electronics. However, most of these conducting films become susceptible to structure fractures under complex deformations or accidental damages, causing the devices to fail to work. Inspired by the self-healing capability of creatures, we developed a self-healing, thermostable, and electrically conducting film that can be healed by electricity by paving aligned carbon nanotube (CNT) sheets onto the surface of liquid crystal elastomer composite films. The aligned CNT sheets make the composites conductive, so the composites can be healed not only by light but also by electricity after breaking. The scratches on the self-healing film can be healed easily under a voltage of 1.18 V/mm because of the electro-thermal effect of aligned CNT sheets. The healed film has almost the same mechanical properties compared to the pristine sample. The electrical and mechanical self-healing of the film is derived from the electrical reconnection of carbon nanotubes and transesterification-induced topology change of the network, respectively. We further demonstrated soft actuators and high-performance supercapacitors based on the prepared self-healing conducting films. This method for preparing self-healing conducting films enables the development of self-healing electronics.

Hybrid perovskite possesses excellent photoelectric properties, including large light-absorption capacity and high carrier mobility, and is an ideal light-absorbing material for photoelectric devices. The grain size and compactness of hybrid perovskite are key factors affecting the performance of photoelectric devices. The photocurrent and photoresponsivity of these devices are relatively low because of the rapidly recombined photoexcited electron-hole pairs in hybrid perovskite. Herein, we develop a facile two-step chemical vapor deposition (CVD) method to synthesize a high-quality van der Waals (vdWs) MAPbI3/graphene heterostructure for high-performance image sensor. We introduced inorganic sources (PbI2) to vdWs epitaxially grown PbI2 film on a seamless graphene monolayer film template through CVD. Methylammonium iodide (MAI) was then reintroduced to prepare the vdWs MAPbI3/graphene heterostructure. The MAPbI3 layer is composed of densely packed, large-size grains and displays a smooth surface. High photoresponsivity of 107 A/W is achieved in the corresponding photodetector. Inspired by the human visual system, we designed a flexible photodetector array containing (24 × 24) pixels, achieving perfect image recognition and color discrimination. Our study may greatly facilitate the construction of high-performance optoelectronic devices in artificial retina, biomedical imaging, remote sensing, and optical communication.

The decrease in friction is often observed in the initial period of sliding a fresh contact between two solid surfaces. This phenomenon is usually termed running-in. Here we report a running-in phe...

The emerging two-dimensional (2D) materials have attracted explosive research interest, because of their unique properties and broad applications. However, the instability of typical 2D materials (...

Skin, the largest organ in the human body, is sensitive to external stimuli. In recent years, an increasing number of skin‐inspired electronics, including wearable electronics, implantable electronics, and electronic skin, have been developed because of their broad applications in healthcare and robotics. Physical sensors are one of the key building blocks of skin‐inspired electronics. Typical physical sensors include mechanical sensors, temperature sensors, humidity sensors, electrophysiological sensors, and so on. In this review, we systematically review the latest advances of skin‐inspired mechanical sensors, temperature sensors, and humidity sensors. The working mechanisms, key materials, device structures, and performance of various physical sensors are summarized and discussed in detail. Their applications in health monitoring, human disease diagnosis and treatment, and intelligent robots are reviewed. In addition, several novel properties of skin‐inspired physical sensors such as versatility, self‐healability, and implantability are introduced. Finally, the existing challenges and future perspectives of physical sensors for practical applications are discussed and proposed.

Silkworm silk, which is obtained from domesticated Bombyx mori ( B. mori ), can be produced in a large scale. However, the mechanical properties of silkworm silk are inferior to its counterpart, spider dragline silk. Therefore, researchers are continuously exploring approaches to reinforce silkworm silk. Herein, we report a facile and scalable hot stretching process to reinforce natural silk fibers obtained from silkworm cocoons. Experimental results show that the obtained hot-stretched silk fibers (HSSFs) retain the chemical components of the original silk fibers while being endowed with increased β -sheet nanocrystal content and crystalline orientation, leading to enhanced mechanical properties. Significantly, the average modulus of the HSSFs reaches 21.6 ± 2.8 GPa, which is about twice that of pristine silkworm silk fibers ( 11.0 ± 1.7 GPa). Besides, the tensile strength of the HSSFs reaches 0.77 ± 0.13 GPa, which is also obviously higher than that of the pristine silk ( 0.56 ± 0.08 GPa). The results show that the hot stretching treatment is effective and efficient for producing superstiff, strong, and tough silkworm silk fibers. We anticipate this approach may be also effective for reinforcing other natural or artificial polymer fibers or films containing abundant hydrogen bonds.

Carbon dots (CDs) are widely studied for years due to their unique luminescent properties and potential applications in many fields. However, aggregation-caused quenching, monotonous emission modes, and unsustainable preparation impose restrictions on their performance and practical applications. Here, this work reports the facile synthesis of sustainable silk-derived multimode emitting CDs with dispersed-state fluorescence (DSF), aggregation-induced fluorescence (AIF), and aggregation-induced room temperature phosphorescence (AIRTP) through radiating sericin proteins in a household microwave oven (800 W, 2.5 min). The structure, luminescent properties, and the mechanism are investigated and discussed. The sericin-derived CDs have graphitized cores and heteroatom-cluster-rich surfaces. The DSF corresponds to the graphitized cores and the AIF origins from the aggregation-induced abundant orbital energy levels on the heteroatom-cluster-rich surfaces. The presence of abundant hydrogen bonds and small gap between the lowest singlet and triplet excited states induces AIRTP. Finally, based on the unique multimode emission of the prepared CDs, their applications in high-performance white-light-emitting diode, information encryption, anti-counterfeiting, and visual humidity sensors are demonstrated.

Layered double hydroxides (LDHs) have lately been hailed as robust lubricant additives for improving tribological properties and as ideal catalysts for synthesizing carbon-based nanomaterials. In this paper, in situ analytical tools are used to track the evolution of the crystal structure and chemical composition of LDHs during calcination. Nickel oxide and elemental nickel can be produced by calcining NiAl-LDH in air (LDH-C-Air) and argon (LDH-C-Ar), respectively. For the base oil with 1 wt % LDH-C-Air, negligible wear can be detected even after a 2 h friction test under a severe contact pressure (∼637 MPa). A relatively thick tribofilm (∼60 nm) with a better mechanical property is formed, which protects the solid surface from severe wear. In addition, the possible formed carbon debris may also prevent the direct collision of asperities and effectively improve the wear resistance. This work provides a unique vision for the application of calcined LDHs with the combination of catalysis and tribology.

Because of the rapid evolution of wearable devices, great effort has been devoted to widely developing flexible strain sensors, as one of the most important components. However, realizing the low-c...

Summary Electronic textile (E-textile) has drawn tremendous attention with the development of flexible and wearable electronics in recent years. Herein, we report the direct printing of E-textile composed of core-sheath fibers by employing a 3D printer equipped with a coaxial spinneret. Customer-designed core-sheath fiber-based patterns can be printed on textile for various purposes. For demonstration, we used carbon nanotubes (CNTs) as a conductive core and silk fibroin (SF) as a dielectric sheath, and fabricated a CNTs@SF core-sheath fiber-based smart pattern, which was further used as a triboelectricity nanogenerator textile. The smart textile could harvest biomechanical energy from human motion and achieve a power density as high as 18 mW/m2. We also demonstrated the printing of a supercapacitor textile for energy storage. The direct printing of smart patterns on textile may contribute to the large-scale production of self-sustainable E-textile with integrated electronics.

With the blooming of wearable technology, developing active materials that can be printed on a large scale has been attracting great attention. Particularly, there are abundant genius structure designs in nature that are endowed with superior performance, inspiring the design of materials for high-performance wearables. Herein, we report the controllable preparation of bionic carbon nanosheets decorated with in situ formed nanoparticles (NP-CNS) through the pyrolysis of calcium gluconate (CG), which are further used for printing high-performance humidity/pressure/strain sensors. The transformation from CG to NP-CNS had been studied in detail. Interestingly, papillae-like CaO NPs are formed on the carbon nanosheets, endowing NP-CNS with good dispersion in inks and rapid response to external stimuli. Particularly, the printed humidity sensor possesses a fast response time (1.7 s) and a broad detection range (0-96% RH), increasing from the high hydroscopicity of the CaO NPs and the thus induced expansion of the NP-CNS. Besides, the strain sensor and pressure sensor also show high sensitivity and broad detection range, which is derived from the unique bionic structure of the NP-CNS. We further showed their excellent performance in monitoring of pulse wave, breath, and human motion, indicating the wide potential applications of the bionic NP-CNS in smart wearables.

Flexible and rechargeable Zn–air batteries, because of their high energy density, low cost, and environmental and human benignity, are one kind of the most attractive energy systems for future wear...

Surface treatment technology is an effective method to reinforce the durability of concrete. In this study, cement-based materials containing industrial solid wastes were modified by hybrid nano-silica (HN), then applied as a novel surface protection material (SPM-HN). The effect of SPM-HN on surface hardness of mortar matrix exposed to seawater was investigated. Further, the microstructure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and mercury intrusion porosimetry (MIP). The results show SPM-HN could significantly enhance the surface hardness of matrix in seawater curing, and the rebound number is increased by 94%.The microstructure analysis demonstrates that the incorporation of HN inhibits the formation of ettringite, thaumasite, and Friedel’s salt. In addition, thermodynamic modeling shows the incorporation of hybrid nano-silica could generate more C-S-H, and decrease the maximum volume of Friedel’s salt when SPM is exposed to seawater. This research indicates SPM-HN can be applied as a concrete protective layer in the marine environment.

Biomass-derived carbon materials (BCMs) are encountering the most flourishing moment because of their versatile properties and wide potential applications. Numerous BCMs, including 0D carbon spheres and dots, 1D carbon fibers and tubes, 2D carbon sheets, 3D carbon aerogel, and hierarchical carbon materials have been prepared. At the same time, their structure-property relationship and applications have been widely studied. This paper aims to present a review on the recent advances in the controllable preparation and potential applications of BCMs, providing a reference for future work. First, the chemical compositions of typical biomass and their thermal degradation mechanisms are presented. Then, the typical preparation methods of BCMs are summarized and the relevant structural management rules are discussed. Besides, the strategies for improving the structural diversity of BCMs are also presented and discussed. Furthermore, the applications of BCMs in energy, sensing, environment, and other areas are reviewed. Finally, the remaining challenges and opportunities in the field of BCMs are discussed.

Protective clothing plays a vital role in safety and security. Traditional protective clothing can protect the human body from physical injury. It is highly desirable to integrate modern wearable electronics into a traditional protection suit to endow it with versatile smart functions. However, it is still challenging to integrate electronics into clothing through a practical approach while keeping the intrinsic flexibility and breathability of textiles. In this work, we realized the direct writing of laser-induced graphene (LIG) on a Kevlar textile in air and demonstrated the applications of the as-prepared Janus graphene/Kevlar textile in intelligent protective clothing. The C═O and N-C bonds in Kevlar were broken, and the remaining carbon atoms were reorganized into graphene, which can be ascribed to a photothermal effect induced by the laser irradiation. Proof-of-concept devices based on the prepared graphene/Kevlar textile, including flexible Zn-air batteries, electrocardiogram electrodes, and NO2 sensors, were demonstrated. Further, we fabricated self-powered and intelligent protective clothing based on the graphene/Kevlar textile. The laser-induced direct writing of graphene from commercial textiles in air conditions provides a versatile and rapid route for the fabrication of textile electronics.

Stretchable and flexible supercapacitors are highly desired due to their many potential applications in wearable devices. However, it is challenging to fabricate supercapacitors that can withstand large tensile strain while maintaining high performance. Herein, we report an ultra-stretchable wire-shaped supercapacitor based on carbon nanotube@graphene@MnO2 fibers wound around a superelastic core fiber. The supercapacitor can sustain tensile strain up to 850%, which is the highest value reported for this type of device to date, while maintaining stable electrochemical performance. The energy density of the supercapacitor is 3.37 mWh·cm–3 at a power density of 54.0 mW·cm–3. The results show that 82% of the specific capacitance is retained after 1,000 stretch–release cycles with strains of 700%, demonstrating the superior durability of the elastic supercapacitor and showcasing its potential application in ultra-stretchable flexible electronics.

Flexible skin-mimicking electronics are highly desired for development of smart human-machine interfaces and wearable human-health monitors. Human skins are able to simultaneously detect different information, such as touch, friction, temperature, and humidity. However, due to the mutual interferences of sensors with different functions, it is still a big challenge to fabricate multifunctional electronic skins (E-skins). Herein, a combo temperature-pressure E-skin is reported through assembling a temperature sensor and a strain sensor in both of which flexible and transparent silk-nanofiber-derived carbon fiber membranes (SilkCFM) are used as the active material. The temperature sensor presents high temperature sensitivity of 0.81% per centigrade. The strain sensor shows an extremely high sensitivity with a gauge factor of ∼8350 at 50% strain, enabling the detection of subtle pressure stimuli that induce local strain. Importantly, the structure of the SilkCFM in each sensor is designed to be passive to other stimuli, enabling the integrated E-skin to precisely detect temperature and pressure at the same time. It is demonstrated that the E-skin can detect and distinguish exhaling, finger pressing, and spatial distribution of temperature and pressure, which cannot be realized using single mode sensors. The remarkable performance of the silk-based combo temperature-pressure sensor, together with its green and large-scalable fabrication process, promising its applications in human-machine interfaces and soft electronics.

Flexible and wearable sensors have drawn extensive concern due to their wide potential applications in wearable electronics and intelligent robots. Flexible sensors with high sensitivity, good flexibility, and excellent stability are highly desirable for monitoring human biomedical signals, movements and the environment. The active materials and the device structures are the keys to achieve high performance. Carbon nanomaterials, including carbon nanotubes (CNTs), graphene, carbon black and carbon nanofibers, are one of the most commonly used active materials for the fabrication of high-performance flexible sensors due to their superior properties. Especially, CNTs and graphene can be assembled into various multi-scaled macroscopic structures, including one dimensional fibers, two dimensional films and three dimensional architectures, endowing the facile design of flexible sensors for wide practical applications. In addition, the hybrid structured carbon materials derived from natural bio-materials also showed a bright prospect for applications in flexible sensors. This review provides a comprehensive presentation of flexible and wearable sensors based on the above various carbon materials. Following a brief introduction of flexible sensors and carbon materials, the fundamentals of typical flexible sensors, such as strain sensors, pressure sensors, temperature sensors and humidity sensors, are presented. Then, the latest progress of flexible sensors based on carbon materials, including the fabrication processes, performance and applications, are summarized. Finally, the remaining major challenges of carbon-based flexible electronics are discussed and the future research directions are proposed.

The unique structure of a vertically aligned carbon nanotube (VACNT) array makes it behave most similarly to a blackbody. It is reported that the optical absorptivity of an extremely black VACNT array is about 0.98-0.99 over a large spectral range of 200 nm-200 μm, inspiring us to explore the performance of VACNT arrays in solar energy harvesting. In this work, we report the highly efficient steam generation simply by laminating a layer of VACNT array on the surface of water to harvest solar energy. It is found that under solar illumination the temperature of upper water can significantly increase with obvious water steam generated, indicating the efficient solar energy harvesting and local temperature rise by the thin layer of VACNTs. We found that the evaporation rate of water assisted by VACNT arrays is 10 times that of bare water, which is the highest ratio for solar-thermal-steam generation ever reported. Remarkably, the solar thermal conversion efficiency reached 90%. The excellent performance could be ascribed to the strong optical absorption and local temperature rise induced by the VACNT layer, as well as the ultrafast water transport through the VACNT layer due to the frictionless wall of CNTs. Based on the above, we further demonstrated the application of VACNT arrays in solar-driven desalination.

With the rapid development of wearable devices, flexible pressure sensors with high sensitivity and wide workable range are highly desired. In nature, there are many well-adapted structures developed through natural selection, which inspired us for the design of biomimetic materials or devices. Particularly, human fingertip skin, where many epidermal ridges amplify external stimulations, might be a good example to imitate for highly sensitive sensors. In this work, based on unique chemical vapor depositions (CVD)-grown 3D graphene films that mimic the morphology of fingertip skin, we fabricated flexible pressure sensing membranes, which simultaneously showed a high sensitivity of 110 (kPa)−1 for 0–0.2 kPa and wide workable pressure range (up to 75 kPa). Hierarchical structured PDMS films molded from natural leaves were used as the supporting elastic films for the graphene films, which also contribute to the superior performance of the pressure sensors. The pressure sensor showed a low detection limit (0.2 Pa), fast response (< 30 ms), and excellent stability for more than 10,000 loading/unloading cycles. Based on these features, we demonstrated its applications in detecting tiny objects, sound, and human physiological signals, showing its potential in wearable electronics for health monitoring and human/machine interfaces.

The increasing demand of wearable electronic devices has promoted the development of high-performance flexible strain sensors which could monitor various physiological parameters. In this work, using silk georgette, which is a commercially available gauzy and lightweight fabric composed of highly twisted yarns in both warp and weft directions as the raw material, an ultrasensitive strain sensor with a wide workable strain range is fabricated through a facile and large-scale process. The obtained strain sensors exhibit remarkable combined features of ultrahigh sensitivity in a wide sensing range (average gauge factor of 29.7 within 40% strain and of 173.0 for a strain of 60–100%), ultralow detection limit (0.01% strain), high durability and stability (10 000 stretching cycles at 100% strain), fast response (

Soft bioelectronics that could be integrated with soft and curvilinear biological tissues/organs have attracted multidisciplinary research interest from material scientists, electronic engineers, and biomedical scientists. Because of their potential human health-related applications, soft bioelectronics require stringent demands for biocompatible components. Silk, as a kind of well-known ancient natural biopolymer, shows unique combined merits such as good biocompatibility, programmable biodegradability, processability into various material formats, and large-scale sustainable production. Such unique merits have made silk popular for intensive design and study in soft bioelectronics over the past decade. Due to the development of fabrication techniques in material processing and progress in research, silk has been engineered into a variety of advanced materials including silk fibers/textiles, nanofibers, films, hydrogels, and aerogels. Natural and regenerated silk materials can also be transformed into intrinsically nitrogen-doped and electrically conductive carbon materials, due to their unique molecular structure and high nitrogen content. The rich morphologies and varied processing options for silk materials can furnish transformed carbon materials with well-designed structures and properties. The favorable and unique material merits of silk materials and silk-derived carbon materials offer potential applications in soft electronics. Based on commercial silk fibers/textiles and the availability of re-engineered silk materials with versatile technological formats, functional soft electronics have been explored with silk as flexible biosupports/biomatrixes or active components. These soft systems include bioresorbable electronics, ultraconformal bioelectronics, transient electronics, epidermal electronics, textile electronics, conformal biosensors, flexible transistors, and resistive switching memory devices. Silk-derived carbon materials with rationally designed morphologies and structures have also been developed as active components for wearable sensors, electronic skins, and flexible energy devices, which provide novel concepts and opportunities for soft electronics. In this Account, we highlight the unique hierarchical and chemical structure of natural silk fibers, the fabrication strategies for processing silk into materials with versatile morphologies and into electrically conductive carbon materials, as well as recent progress in the development of silk-based advanced materials (silk materials and silk-derived carbon materials) for soft bioelectronics. The design and functionality of soft electronics developed with commercial silk fibers/textiles, re-engineered silk materials, and silk-derived carbon materials as biosubstrate/matrix and active components is introduced in detail. We further discuss future challenges and prospects for developing silk-based soft bioelectronics for wearable healthcare systems. By leveraging the unique advantages of silk-based advanced materials, the design and construction strategy for flexible electronics, as well as the potential of flexible electronics for conformable and intimate association with human tissues/organs, silk-based soft bioelectronics should have a significant impact on diverse healthcare fields.

Flexible enzymatic glucose sensors have been investigated extensively for health monitoring systems. However, enzymatic glucose sensors have some problems, such as poor stability and complicated immobilization procedures. Rational and controllable design of nanomaterials with a unique structure, high activity and good electrochemical performance for nonenzymatic glucose sensors is desired critically. In this paper, we synthesize cuprous oxide nanoparticles embedded in carbon spheres directly on carbonized silk fabrics (Cu2O NPs@CSs/CSF), which is further used for the fabrication of a flexible and self-supported non-enzymatic glucose sensor. The Cu2O NPs@CSs/CSF shows good electrical conductivity due to the large contact area and the stable connection between the carbonized silk fabrics and carbon spheres. We demonstrate that the as-obtained non-enzymatic glucose sensor possesses high sensitivity and good stability, indicating its potential for practical applications. This strategy diversifies the toolbox available to the field of nonenzymatic glucose sensors and holds promise for flexible electronic devices.

Graphene layers grown on metallic substrates by chemical vapor deposition generally exhibit wrinkles due to mismatches in thermal expansion coefficients of the graphene and the substrates, which affect remarkably the tribological, mechanical and electrical properties of graphene-based devices. Here we report an isotropic-stretching method to eliminate these wrinkles. The morphology evolution of the wrinkles during the stretching process is studied using an atomic force microscope, and a simple method for calculating the critical strain required to eliminate the wrinkles is suggested. Friction and scratching tests demonstrate that for graphene layers the friction and anti-wear performances of regions with eliminated pre-existing wrinkles are as good as the wrinkle-free regions. Our method is expected to be applicable to other layered materials grown on deformable surfaces.

Single-crystal graphene domains grown by chemical vapor deposition (CVD) intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the formation of graphene with different shapes. Here we report the growth of oriented large-area pentagonal single-crystal graphene domains on Cu foils by CVD. We found that high-index Cu planes contributed selectively to the formation of pentagonal graphene. Our results indicated that lattice steps present on the crystalline surface of the underlying Cu promoted graphene growth in the direction perpendicular to the steps and finally led to the disappearance of one of the edges forming a pentagon. In addition, hydrogen promoted the formation of pentagonal domains. This work provides new insights into the mechanism of graphene growth.

The development of nanomaterials has put forward high requirements for characterization techniques. Optical microscopy (OM), with easy accessibility and open operating spaces as compared to scanning electron microscopy, is a good choice to quickly locate materials and to be integrated with other equipment. However, OM is limited by its low resolution. Herein, we present a facile and non-destructive approach for optical observation of nanomaterials under conventional OMs with the aid of volatile nanoparticles (NPs), which can be deposited and removed in a controlled manner. The NPs deposited on the surface of nanomaterials render strong light scattering to enable the nanomaterials to become optically visible. For example, this approach enables the observation of individual carbon nanotubes (CNTs) with OMs at low magnification or even with the naked eye. Both supported CNTs on various substrates and suspended CNTs can be observed with this approach. Most importantly, the NPs can be completely removed through moderate heat treatment or laser irradiation, avoiding potential influence on the properties or subsequent applications of nanomaterials. Furthermore, we systematically investigate the deposition of various volatile NPs (up to 14 kinds) for the optical observation of nanomaterials. We also demonstrated the application of this approach on other nanomaterials, including nanowires and graphene. We showed that this approach is facile, controllable, non-destructive, and contamination-free, indicating wide potential applications.

Controlled synthesis of highly efficient, stable, and cost-effective oxygen reaction electrocatalysts with atomically-dispersed Me-N

Silk has outstanding mechanical properties and biocompatibility. It has been used to fabricate traditional textiles for thousands of years and can be produced in large scale. Silk materials are potentially attractive in modern textile electronics. However, silk is not electrically conductive, thus limiting its applications in electronics. Moreover, regenerated silk is generally rigid and brittle, which hinder post processing. Here we report the fabrication of conductive silk wire in which carbon nanotube (CNT) yarns are wrapped with fluffy and flexible silk nanofiber films. The silk nanofiber film was prepared by electrospinning and then wrapped around a rotating CNT yarn in situ. The obtained silk-sheathed CNT (CNT@Silk) wire has an insulating sheath, which protects the body against electrical shock. In addition, the fabricated wires exhibit a high electrical conductivity (3.1 × 104 S/m), good mechanical strength (16 cN/tex), excellent flexibility, and high durability. More importantly, the wires have an...

Developing a simple and industrially scalable method to produce graphene with high quality and low cost will determine graphene's future. The two conventional approaches, chemical vapor deposition and liquid-phase exfoliation, require either costly substrates with limited production rate or complicated post treatment with limited quality, astricting their development. Herein, an extremely simple process is presented for synthesizing high quality graphene at low-cost in the gas phase, similar to "snowing," which is catalyst-free, substrate-free, and scalable. This is achieved by utilizing corona discharge of SiO2 /Si in an ordinary household microwave oven at ambient pressure. High quality graphene flakes can "snow" on any substrate, with thin-flakes even down to the monolayer. In particular, a high yield of ≈6.28% or a rate of up to ≈0.11 g h-1 can be achieved in a conventional microwave oven. It is demonstrated that the snowing process produces foam-like, fluffy, 3D macroscopic architectures, which are further used in strain sensors for achieving high sensitivity (average gauge factor ≈ 171.06) and large workable strain range (0%-110%) simultaneously. It is foreseen that this facile and scalable strategy can be extended for "snowing" other functional 2D materials, benefiting their low-cost production and wide applications.

The last decade has seen the rapid growth of research on two-dimensional (2D) materials, represented by graphene, but research on their thermophysical properties is still far from sufficient owing to the experimental challenges. Herein, we report the first measurement of the specific heat of multilayer and monolayer graphene in both supported and suspended geometries. Their thermal conductivities were also simultaneously measured using a comprehensive Raman optothermal method without needing to know the laser absorption. Both continuous-wave (CW) and pulsed lasers were used to heat the samples, based on consideration of the variable laser spot radius and pulse duration as well as the heat conduction within the substrate. The error from the laser absorption was eliminated by comparing the Raman-measured temperature rises for different spot radii and pulse durations. The thermal conductivity and specific heat were extracted by analytically fitting the temperature rise ratios as a function of spot size and pulse duration, respectively. The measured specific heat was about 700 J (kg K)^ at room temperature, which is in accordance with theoretical predictions, and the measured thermal conductivities were in the range of 0.84–1.5 × 10^3 W (m K)^. The measurement method demonstrated here can be used to investigate in situ and comprehensively the thermophysical properties of many other emerging 2D materials.

The prosperous development of stretchable electronics poses a great demand on stretchable conductive materials that could maintain their electrical conductivity under tensile strain. Previously reported strategies to obtain stretchable conductors usually involve complex structure-fabricating processes or utilization of high-cost nanomaterials. It remains a great challenge to produce stretchable and conductive materials via a scalable and cost-effective process. Herein, a large-scalable pyrolysis strategy is developed for the fabrication of intrinsically stretchable and conductive textile in utilizing low-cost and mass-produced weft-knitted textiles as raw materials. Due to the intrinsic stretchability of the weft-knitted structure and the excellent mechanical and electrical properties of the as-obtained carbonized fibers, the obtained flexible and durable textile could sustain tensile strains up to 125% while keeping a stable electrical conductivity (as shown by a Modal-based textile), thus ensuring its applications in elastic electronics. For demonstration purposes, stretchable supercapacitors and wearable thermal-therapy devices that showed stable performance with the loading of tensile strains have been fabricated. Considering the simplicity and large scalability of the process, the low-cost and mass production of the raw materials, and the superior performances of the as-obtained elastic and conductive textile, this strategy would contribute to the development and industrial production of wearable electronics.

Tremendous progress has been made in the research of carbon nanotubes (CNTs) in the past 25 years, which has facilitated the progress and development of fundamental research and industrial applications. However, challenges and opportunities remain. At the same time, the discovery and development of graphene in 2004 has had an obvious impact on the applications of CNTs. The progress and development of CNTs provide valuable references for graphene, ranging from synthesis and characterization to applications. Promising materials combining CNTs and graphene are on the rise. The popularity of CNT/graphene hybrids has expanded research and application of carbon nanomaterials. In this chapter, we summarize the challenges and opportunities that exist in the synthesis and application of CNTs and describe the synthesis and application of CNT/graphene hybrid materials.

Controlled synthesis of highly efficient, stable, and cost-effective oxygen reaction electrocatalysts with atomically-dispersed Me-Nx -C active sites through an effective strategy is highly desired for high-performance energy devices. Herein, based on regenerated silk fibroin dissolved in ferric chloride and zinc chloride aqueous solution, 2D porous carbon nanosheets with atomically-dispersed Fe-Nx -C active sites and very large specific surface area (≈2105 m2 g-1 ) are prepared through a simple thermal treatment process. Owing to the 2D porous structure with large surface area and atomic dispersion of Fe-Nx -C active sites, the as-prepared silk-derived carbon nanosheets show superior electrochemical activity toward the oxygen reduction reaction with a half-wave potential (E1/2 ) of 0.853 V, remarkable stability with only 11 mV loss in E1/2 after 30 000 cycles, as well as good catalytic activity toward the oxygen evolution reaction. This work provides a practical and effective approach for the synthesis of high-performance oxygen reaction catalysts towards advanced energy materials.

A novel carbonized plain-weave silk-fabric-based wearable strain sensor is proposed by Y. Y. Zhang and co-workers on page 6640. The sensor can be stretched up to 500% with high sensitivity in a wide strain range and can be assembled into wearable devices for the detection of both large and subtle human activities, showing great potential in human-motion detection and robotics.

A carbonized plain-weave silk fabric is fabricated into wearable and robust strain sensors, which can be stretched up to 500% and show high sensitivity in a wide strain range. This sensor can be assembled into wearable devices for detection of both large and subtle human activities, showing great potential for monitoring human motions and personal health.

Flexible and wearable electronics are attracting wide attention due to their potential applications in wearable human health monitoring and care systems. Carbon materials have combined superiorities such as good electrical conductivity, intrinsic and structural flexibility, light weight, high chemical and thermal stability, ease of chemical functionalization, as well as potential mass production, enabling them to be promising candidate materials for flexible and wearable electronics. Consequently, great efforts are devoted to the controlled fabrication of carbon materials with rationally designed structures for applications in next-generation electronics. Herein, the latest advances in the rational design and controlled fabrication of carbon materials toward applications in flexible and wearable electronics are reviewed. Various carbon materials (carbon nanotubes, graphene, natural-biomaterial-derived carbon, etc.) with controlled micro/nanostructures and designed macroscopic morphologies for high-performance flexible electronics are introduced. The fabrication strategies, working mechanism, performance, and applications of carbon-based flexible devices are reviewed and discussed, including strain/pressure sensors, temperature/humidity sensors, electrochemical sensors, flexible conductive electrodes/wires, and flexible power devices. Furthermore, the integration of multiple devices toward multifunctional wearable systems is briefly reviewed. Finally, the existing challenges and future opportunities in this field are summarized.

Wearable heaters have attracted broad attention due to their applications in personal heating systems and healthcare management, such as heat preservation in textile/clothing and thermotherapy. Protecting heating performance against deterioration under large deformation is is important for the application of wearable heaters. Here, a highly stretchable electrically driven heater based on electrically conductive weft-knitted fabrics is reported, which can be transformed from traditional fabrics through a facile heat treatment process. As an example, a heater made from Modal shows a heating temperature higher than 100 °C at a driving voltage as low as 3 V. The Joule heating performance of the heater does not deteriorate even under a large strain of 70%. Furthermore, according to theoretical analysis and experimental results, the output power and saturated temperature of the heater under a certain voltage can be easily tuned by tailoring the shape and size of the fabric to meet customized demands. The superior performance of the heater originates from the weft-knitted structural configuration. Finally, the application of the ultrastretchable heater in wearable thermal therapy devices is demonstrated, showing its great potential in wearable electronics.